Biological Treatment of Pulp and Paper Mill Effluents

The pulp and paper industry is one of the major consumers of water. Pulp and paper industrial wastewaters usually contain halogenated organic materials, because general use is made of chlorine-containing compounds as bleaching agents during pulp and paper manufacture. Kraft pulping is the most common commercial chemical delignification procedure. Chlorination is generally the first stage in kraft pulping and during this treatment phase, chlorinated organic compounds are produced. The chlorinated substances are extracted with dilute alkali from the pulp in the subsequent extraction phase. Chloro-organic compounds tend to persist in nature because of their inherent recalcitrance; they are often toxic to aquatic live; many are genotoxic and have the potential to migrate widely throughout the ecosystem, ultimately accumulating in the fatty tissues of organisms. Legislation has been introduced to limit the levels of these toxic compounds in effluents. Additionally, during bleaching treatments chromophoric, highly oxidized, polymeric lignin/chlorolignin derivatives are formed that give rise to a dark color in the effluent. The color poses an aesthetic problem and contributes to the biological oxygen demand. Several methods have been attempted for decolorization and detoxification of bleached kraft effluents. These include physicochemical and biotechnological methods. The problems underlying the physicochemical treatments are those associated with cost and reliability. Biotechnological methods have the potential to eliminate/ reduce the problems associated with physicochemical methods. This article reviews the research on the use of Biotechnological methods for treatment of pulp and paper mill effluents. The progress made and the further scope are also discussed.